Crusader Kings 2: Monks and Mystics

Open or secret societies are introduced in this expansion for Crusader Kings II, which adds Monastic orders and cults, with many ways for rulers and would-be rulers to rise through their ranks, purge their enemies and otherwise manipulate civilisation at large.
Many more options will be open to you including more Councillor actions to cement influence and power, and for new events and acts of intrigue with assassins, archaeological pursuits, holy relics and the unearthing of great treasures. Harmony is a good thing for a nation but only when you're holding the reins.